The broad goals of this project are to understand the control of enzyme formation in biosynthetic pathways, particularly of those in arginine synthesis and methionine synthesis in Escherichia coli. Recently a cell-free system has been developed for the synthesis of one of the arginine enzymes, acetylornithinase. As a source of DNA, a transducing phage carrying the structural gene (argE) for this enzyme has been obtained. In the future, details of the biochemical mechanism of repression are to be studied in this system and in systems involving two enzymes of methionine synthesis, the non-B12 transmethylase (metE) and folate reductase (metF). Such details include isolation and characterization of the repressors, binding of the repressor to operator sites for various structural genes, determination of the nature of the corepressors and test for repression at the levels of transcription and translation. A phage carrying the structural gene for the feedback enzyme of the arginine pathway has been isolated and will be used in an effort to obtain and characterize this enzyme in cell-free extracts.